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Abstract:

In one embodiment, the present invention relates to a non-woven fiber
assembly comprising one or more fibers wherein each fiber contains: a
hydrophilic component; and an elastomeric component, and wherein the
non-woven fiber assembly further comprises an adhesive component. In
still another embodiment, the present invention relates to a non-woven
fiber assembly comprising one or more fibers wherein each fiber contains:
a hydrophilic component; an elastomeric component; and an adhesive
component, wherein the hydrophilic component, the elastomeric component
and the adhesive component are all contained within each fiber. Also
disclosed is a method of making the afore-mentioned non-woven fiber
assemblies. Additionally, a medical dressing made from the non-woven
fiber assemblies of the present invention is disclosed.

21. The non-woven fiber assembly of claim 16, wherein the at least one
fiber has a diameter of between about 3 nanometers and about 3000
nanometers.

22. The non-woven assembly of claim 16, wherein the adhesive component is
located on, or in proximity to, the one or more fibers.

23. A method of making a non-woven fiber assembly, the method comprising
the steps of:providing at least one fiber-forming material; andforming at
least one fiber from the at least one fiber-forming material, andwherein
the at least one fiber forming material comprises a hydrophilic
component, an elastomeric component, and optionally an adhesive
component, and wherein each fiber contains a hydrophilic component and an
elastomeric component, and optionally contains an adhesive component.

24. The method of claim 23, wherein the relative amounts of the adhesive
component, the elastomeric component, and the hydrophilic component
varies over time, thereby producing a fiber assembly in which the
composition of the one or more fibers at a first surface of the dressing
differs from the composition of the one or more fibers at a second
surface of the dressing.

25. A method of treating a patient comprising:applying a non-woven fiber
assembly of claim 16 to a predetermined area of the patient.

Description:

BACKGROUND OF THE INVENTION

[0001]This invention relates to composite fiber assemblies. More
particularly, this invention relates to composite nanofiber assemblies
that can be produced from a polymeric matrix material.

[0002]Various techniques are known in the textile field for the creation
of fibers. Melt-blowing, the nanofibers by gas jet (NGJ) technique, and
electrospinning are included among these techniques. In a melt-blowing
process, a stream of molten polymer or other fiber-forming material is
typically extruded into a jet of gas to form fibers. The resulting fibers
are typically greater than 1,000 nanometers in diameter, and more
typically, greater than 10,000 nanometers in diameter.

[0003]A technique and apparatus for forming fibers having a diameter of
less than 3,000 nanometers according to the NGJ technique is described in
U.S. Pat. Nos. 6,382,526 and 6,520,425, the disclosures of which are
hereby incorporated by reference.

[0004]The electrospinning of liquids and/or solutions capable of forming
fibers, also known within the fiber forming industry as electrostatic
spinning, is well known and has been described in a number of patents as
well as in the general literature. The process of electrospinning
generally involves the creation of an electrical field at the surface of
a liquid. The resulting electrical forces create a jet of liquid that
carries electrical charge. Thus, the liquid jets may be attracted to
other electrically charged objects at a suitable electrical potential. As
the jet of liquid elongates and travels, it will harden and dry. The
hardening and drying of the elongated jet of liquid may be caused by
cooling of the liquid, i.e., where the liquid is normally a solid at room
temperature; evaporation of a solvent, e.g., by dehydration, (physically
induced hardening); or by a curing mechanism (chemically induced
hardening). The produced fibers are collected on a suitably located,
oppositely charged receiver and subsequently removed from it as needed,
or directly applied to an oppositely charged or grounded generalized
target area.

[0005]Fibers produced by this process have been used in a wide variety of
applications, and are known, from U.S. Pat. No. 4,043,331 to be
particularly useful in forming non-woven mats suitable for use in wound
dressings. One of the major advantages of using electrospun fibers in
wound dressings, is that very thin fibers can be produced having
diameters, usually on the order of about 50 nanometers to about 25
microns, and more preferably, on the order of about 50 nanometers to
about 5 microns. These fibers can be collected and formed into non-woven
mats of any desired shape and thickness. It will be appreciated that,
because of the very small diameter of the fibers, a mat with very small
interstices and high surface area per unit mass, two characteristics that
are important in determining the porosity of the mat, can be produced.

[0006]Medical dressings formed using non-woven mats of these polymeric
fibers may provide particular benefits depending upon the type of polymer
or polymers used, as taught by U.S. Pat. No. 4,043,331. A wettable, or
hydrophilic, polymer, such as, for example, a polyurethane may be used,
or a non-wetting, or at least weakly hydrophobic, polymer such as, for
example, a saturated polyester, may be employed. Where the dressing is
formed from a wettable polymer, blood or serum escaping from the wound
tends to penetrate the dressing and the high surface area encourages
clotting. Such dressings could be used as emergency dressings to halt
bleeding. On the other hand, where the dressing is formed from a
non-wetting polymer, and if the interstices between the fibers are
sufficiently small, i.e., on the order of less than about 100 nanometers,
tissue fluids, including blood, tend not to permeate the dressing.
Consequently, the fluids are retained adjacent to the wound where
clotting will occur. Subsequent removal of such a dressing is facilitated
by the absence of blood clots permeating the dressing material. Still
further, U.S. Pat. No. 4,043,331 suggests that such dressings have the
advantage that they are usually sufficiently porous to allow interchange
of oxygen and water vapor between the atmosphere and the surface of the
wound.

[0007]Besides providing variability as to the diameter of the fibers or
the shape, thickness, or porosity of any non-woven mat produced
therefrom, the ability to electrospin the fibers also allows for
controlled variations in the composition of the fibers, their density of
deposition and their inherent strength. The above-identified U.S. patent
indicates that it is also possible to post-treat the non-woven mats with
other materials to modify their properties. For example, one could
increase the strength of the mat using an appropriate binder or increase
water resistance by post-treating the mat with silicone or other
water-resistant material, such as perfluoro alkyl methacrylate.
Alternatively, strength may be increased by utilizing fibers of
polytetrafluoroethylene (PTFE).

[0008]By varying the composition of the fibers being formed, fibers having
different physical or chemical properties may be obtained. This can be
accomplished either by spinning a liquid containing a plurality of
components, each of which may contribute a desired characteristic to the
finished product, or by simultaneously spinning, from multiple liquid
sources, fibers of different compositions that are then simultaneously
deposited to form a mat. The resulting mat, of course, would consist of
intimately intermingled fibers of different material. A further
alternative noted in the above-referenced U.S. patent is to produce a mat
having a plurality of layers of different fibers of different materials
(or fibers of the same material but different characteristics, e.g.
diameter), as by, for example, varying the type of fibers being deposited
on the receiver over time. For example, wettable and non-wetting polymers
each offer additional properties that may be desirable in different
applications. Wettable polymers tend to be highly absorbent but provide
mats that are relatively weak, while non-wetting polymers tend to be
non-absorbent but provide mats that are relatively strong. In some
applications, such as medical dressings, for example, it may be desirable
to use a combination of wettable and non-wetting polymer layers in a
single article. The wettable polymer layer or layers contribute a
relatively high level of absorbency to the article while the non-wetting
polymer layer or layers contribute a relatively high level of strength.
Use of such a laminate-type structure, however, suffers from the
disadvantage that the hydrophobic layer can form a barrier to liquids and
interfere with the absorption of liquid by the wettable layer.
Additionally, upon absorption of liquid, the wettable polymer layer will
weaken and misalignment, slipping, or even separation of the layers may
occur, resulting in failure of the integrity of the article.

[0009]U.S. Pat. No. 4,043,331 indicates that strong, non-woven mats
comprising a plurality of fibers of organic, namely polymeric, material
may be produced by electrostatically spinning the fibers from a liquid
consisting of the material or its precursor. These fibers are collected
on a suitably charged receiver. The mats or linings formed on the
receiver can then be transferred and used alone or in conjunction with
other previously constructed components such as, for example, mats of
woven fibers and backing layers to provide a wound dressing of desired
characteristics. For instance, in producing wound dressings, additional
supports or reinforcement such as mats or linings of fibers, or backing
layers may be required in order to adhere the wound dressing to the skin
and to provide other desirable properties to the wound dressing. As an
example, a mat or lining of woven fibers may contain materials having
antiseptic or wound-healing properties. Surface treatments of the already
formed non-woven mats may also provide added benefits in the production
of such wound dressings. However, U.S. Pat. No. 4,043,331 does not
provide a medical dressing that adheres to undamaged skin only. It also
does not provide a single-component dressing that can adhere to a desired
area of a patient, or a dressing comprised of composite fibers that vary
in their composition along their length.

[0010]It has also been described in PCT International Publication No.
WO98/03267 to electrostatically spin a wound dressing in place over a
wound. In such a use, the body itself is grounded and acts as a collector
of the electrospun fibers. This method of synthesizing a wound dressing
allows for solution of some of the problems associated with bandage and
gauze storage and preparation. It is well known for example, that gauze
and bandages must be stored and maintained in a sterile environment in
order to offer the greatest protection in healing wounds. If the gauze or
bandages are not sterile, these products offer little help in protecting
the wound. Electrospinning a wound dressing in place, over a wound, from
a sterile liquid, eliminates these problems.

[0011]Electrospinning a wound dressing in place over a wound, however,
limits the types of solvents that may be used to only those solvents that
are compatible with the skin or other tissue to which the dressing is
applied. Examples of such solvents include water, alcohols, and acetone.
Likewise, because the types of usable solvents are limited, the types of
additives, such as, for example, absorbents, bactericides, and
antibiotics, that may be used in conjunction with the polymer are also
limited to those that are soluble, or form a stable dispersion in the
particular solvent used. Similarly, the types of polymers that may be
used are also limited to those that are soluble in a skin- or
tissue-compatible solvent. Biocompatible polymer/solvent combinations
include, for example, poly(ethylenimine)/ethanol,
poly(vinylpyrrolidone)/ethanol, polyethylene oxide/water, and
poly(2-hydroxymethacrylate)/ethanol+acid. While fibers from such a
combination are non-reactive in their state as spun, exposure of the
fibers to fluids, either from a wound or from external sources, may cause
a local pH change from a neutral or nearly neutral pH to one that is
acidic or alkaline, depending on the composition of the fiber. For
example, when poly(ethylenimine) fiber is exposed to fluid, it will
participate in proton transfer, resulting in an alkaline pH in the fluid
contacting the polymer. The creation of an undesirable pH environment may
cause side effects, such as slow wound healing.

[0012]An electrospun fiber containing a substantially homogeneous mixture
of a hydrophilic polymer, a polymer which is at least weakly hydrophobic,
and optionally, a pH adjusting compound has been described in
International Publication No. WO 01/27365, the disclosure of which is
incorporated herein by reference. The fibers may be deposited directly on
their intended usage area without first applying the fibers to a
transient, charged receiver or subjecting it to other intermediate
fabrication steps. The resulting fibers, however, do not provide a
dressing which adheres to undamaged skin only.

[0013]Therefore, the need continues to exist for a medical dressing or
other non-woven mat or membrane that is capable of adhering to a dry
substrate but will not adhere to a wet surface such as a wound or to wet
tissues that form in the early stages of wound healing. A need also
exists for a medical dressing that can provide properties resulting from
a variation in the composition of the individual fibers of the dressing
over their length.

BRIEF SUMMARY OF THE INVENTION

[0014]It is, therefore, an aspect of the present invention to provide a
medical dressing or other non-woven mat or membrane that is capable of
adhering to a dry substrate such as undamaged skin but will not adhere to
a wet substrate such as the surface of a wound or to wet tissues that
form in the early stages of wound healing.

[0015]It is also an aspect of the present invention to provide a method of
making a medical dressing that is capable of adhering to undamaged skin
but will not adhere to the wet surface of a wound or to wet tissues that
form in the early stages of wound healing.

[0016]It is a further aspect of the present invention to provide a medical
dressing that contains composite fibers that vary in their composition
over their length.

[0017]In general, the present invention provides a non-woven fiber
assembly comprising one or more fibers, wherein the fibers contain an
adhesive component, an elastomeric component and a hydrophilic component.

[0018]The present invention also provides a method of making a non-woven
fiber assembly. The method comprises the steps of providing at least one
fiber-forming material and forming at least one fiber from said at least
one fiber-forming material, wherein the at least one fiber forming
material comprises an adhesive component, an elastomeric component, and a
hydrophilic component.

[0019]The present invention also provides a method of treating a patient
comprising applying a non-woven fiber assembly to a predetermined area of
the patient, wherein the non-woven fiber assembly contains one or more
fibers comprising an adhesive component, an elastomeric component, and a
hydrophilic component.

[0020]The present invention also provides an apparatus for forming at
least one composite fiber, the fiber comprising a hydrophilic component,
an elastomeric component and an adhesive component, wherein the apparatus
comprises a plurality of reservoirs for containing more than one type of
fiber-forming material, a plurality of valves, each independently in
communication with a reservoir, and a fiber-forming device selected from
the group consisting of a spinnerette, a NGJ nozzle, and an
electrospinning device, in communication with said valves.

BRIEF DESCRIPTION OF THE DRAWING

[0021]FIG. 1 is a schematic representation of an apparatus for forming
composite fibers according to the present invention.

[0022]FIG. 2 is a graph showing the absorbency of nanofiber assemblies of
the present invention.

[0023]FIG. 3 is a stress-strain curve for nanofiber assemblies of the
present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0024]As mentioned above, the present invention provides a non-woven fiber
assembly comprising at least one fiber and containing an adhesive
component, an elastomeric component, and a hydrophilic component. The at
least one fiber may contain a series of segments such as a segment that
is primarily or even totally an adhesive component, a segment that is
primarily or totally an elastomeric component, and a segment that is
primarily or totally a hydrophilic component. When the at least one fiber
has such an arrangement of components, the different segments may be
arranged in any of a number of orders, depending on the needs of a
particular application. It is envisioned that a particularly useful
arrangement would include a segment that is at least primarily an
adhesive component located adjacent to a segment that is at least
primarily a hydrophilic component, which is, in turn, located adjacent to
segment that is at least primarily an elastomeric component. The
composite fiber may also include two or more components in a segment of
fiber. The composition of each segment and number of segments may also
vary over the length of the fiber. Additionally, the transition between
segments may be either smooth or abrupt. Alternatively, the composition
of the fiber may be constant over its length. The non-woven fiber
assembly may also comprise a plurality of fibers wherein different
fibers, individually or in combination, supply each component.

[0025]The method of making a non-woven fiber assembly, according to the
present invention, includes the forming of at least one fiber, the at
least one fiber containing an adhesive component, an elastomeric
component, and a hydrophilic component. The at least one fiber may be
formed by any technique that is compatible with each of the components of
the fiber or fibers. It is envisioned that melt-blowing, the NGJ
technique, and electrospinning are suitable methods for forming fibers
according to the present invention. Electrospinning provides particular
advantages. Fibers may also be formed by other techniques, including
phase separation, casting in pores, and slitting of a film.

[0026]As discussed above, one of the major advantages of using
electrostatically spun fibers in non-woven fiber assembly, is that these
fibers can be produced having very small diameters, usually on the order
of about 3 nanometers to about 3000 nanometers, and more preferably, on
the order of about 10 nanometers to about 500 nanometers, and most
preferably, on the order of about 10 nanometers to about 100 nanometers.
Fibers formed by the NGJ technique also have very small diameters. Thus,
given that these "nanofibers" can be formed into non-woven membranes of
any desired shape and thickness relatively rapidly, their usefulness and
desirability in medical dressings and other non-woven fiber assembly's
can readily be appreciated.

[0027]When fibers having very small diameters are formed, a membrane with
very small interstices and high surface area is produced. Non-woven fiber
assemblies according to this invention, may be useful in medical
dressings, diapers, feminine hygiene products, absorbent towels or wipes
for the skin, and transdermal or oral delivery systems for therapeutic
and prophylactic substances. It is also envisioned that the non-woven
fiber assemblies may also be used for other purposes such as spill
management, water transport and management in fuel cells, and for
collecting and transporting water or other fluids from coalescence
filters.

[0028]When the non-woven fiber assembly forms a medical dressing, the
resultant medical dressing is microporous and breathable, but is
resistant to high airflow. These are important and desirable
characteristics of medical dressings. Generally, pores sizes for the
medical dressing produced using such techniques range from about 50
nanometers to about 1 micron, small enough to protect the wound from
bacterial penetration via aerosol particle capture mechanisms. Pore sizes
in this range may also at least partially hinder the passage of viral
particles through the dressing to the wound.

[0029]The non-woven mats or membranes of the present invention preferably
have high surface areas of at least 5 m2/g, and more preferably,
approximately 100 m2/g for efficient fluid absorption and dermal
delivery. The high surface areas may also impart high hemostatic
potential for the dressing.

[0030]When used as a medical dressing, the non-woven fiber assembly of the
present invention provides greater water vapor permeability, as expressed
by water vapor flux, than commercial barrier films. In one embodiment,
the electrospun membrane forms a medical dressing that has a water vapor
flux at least ten fold greater than that of solid film barrier dressings.
Preferably, the medical dressing provides at least 30-fold greater water
vapor flux than a commercial barrier film. More preferably, the medical
dressing provides at least 30-fold greater water vapor flux than a
commercial barrier film.

[0031]The medical dressing is a thin but effective barrier to
contaminants. The appropriate thickness of the fibers of the dressing
depends on factors such as the fiber-forming materials used the diameter
of the fibers, the structural arrangement of the fibers, the size of the
pores formed by the fibers as well as the desired degree of air
permeability and protection from contaminants. For example, the fibers
may form a medical dressing when applied at a coating level of as little
as about 0.1 g/m2. The fibers may also be applied at a coating level
of between about 0.1 and 100 gm/m2. At one thickness, the fibers of
the medical dressing provide greater than 97 percent filtration
efficiency against aerosols between about 0.5 μm and about 20 μm in
diameter. At another thickness, the fibers provide greater than 97
percent filtration efficiency against aerosols between about 0.1 μm
and about 20 μm in diameter. The fibers may also be applied at a
thickness which provides for substantially complete filtration of
aerosols between about 0.5 and about 20 μm in diameter or even about
0.1 μm to about 20 μm in diameter.

[0032]While the medical dressing protects against contamination, it does
so while allowing the passage of air. This allows penetration of oxygen
through the dressing to a wound, burn, or other protected area, thereby
permitting accelerated healing and a decreased likelihood of infection
compared to wound dressings that do not permit airflow to the protected
area. In one example, the medical dressing provides an airflow resistance
of less than 5×109 m-1. Preferably, the medical dressing
has an air flow resistance of less than 2×108 m-1. In
another example, the medical dressing has an air flow resistance of less
than 2×107 m-1.

[0033]The fibers and the resultant medical dressings and other non-woven
fiber assemblies of the present invention are lightweight, oxygen and
moisture permeable, yet protect against airborne contaminants such as
dust, microbes, or other infectious agents. The ability of the membrane
fibers to transport and deliver therapeutic additives to the site of a
wound is also important. This ability to transport and deliver additives
can be controlled through the choice of polymer carrier, density and
thickness of the non-woven sheet of fibers, and/or layering of different
membrane fiber compositions.

[0034]With respect to the fibers used in a medical dressing, it will be
understood that the fibers may preferably be dry, and form strong
membranes. However, in some instances, a wet fiber may be employed.
Although wet fibers may be strong, wet fibers are generally softer and
conform to the surface of the substrate to which they are applied better
than dry fibers. Other advantages may include those set forth previously
in discussion above of U.S. Pat. No. 4,043,331. In any event, the ability
to form the fibers of the present invention directly onto the surface of
a wound allows for improved flexibility in the composition of the fibers,
improved porosity of the membrane, and improved strength, all in an
inexpensive and timely manner. Moreover, the direct application of the
fibers means that the fibers can be advantageously placed in intimate,
and shape forming, contact with the total wound surface. This enables
efficient removal of dead cells, fluid or bacteria from deep within the
wound when the dressing is changed, thereby reducing or eliminating the
need for debridement of the wound. Direct contact with the surface of the
wound will also enable improved drug delivery to the wound. Finally, it
will be appreciated that direct application provides for improved and, in
fact, inherent, sterility of the fibers and, therefore, the dressing,
thereby eliminating the need for gamma radiation or other treatments to
disinfect the dressing materials. In addition, controlled generation of
ozone and other active species may be used to assist with sterilization.

[0035]In one embodiment, the dressing also comprises a closed cell foam to
protect the treated area against mechanical disturbance or to provide
thermal insulation.

[0036]The non-woven fiber assembly of the present invention may include at
least one fiber formed from a mixture of any of a variety of a
hydrophilic polymers, elastomeric polymers, and polymers having adhesive
properties. The fiber-forming material can be optionally blended with any
of a number of medically important wound treatments, including analgesics
and other pharmaceutical or therapeutic additives. Such polymeric
materials suitable for electrospinning into fibers may include, for
example, those inert polymeric substances that are absorbable and/or
biodegradable, that react well with selected organic or aqueous solvents,
or that dry quickly. Essentially any organic or aqueous soluble polymer
or any dispersions of such polymer with a soluble or insoluble additive
suitable for topical therapeutic treatment of a wound may be employed.
When used in applications other than medical dressings, other additives
may be used. For example, in spill management applications, particles
useful for absorbing a particular type of compound may be encapsulated in
one of the polymer components. For example, a non-woven fiber assembly
that is useful for managing spills of hydrophobic compounds may have a
compound that absorbs hydrophobic compounds encapsulated within one of
the polymeric components of the assembly.

[0037]The dressing of the present invention may include a mixture of
nanofibers that are elastomeric and either hydrophilic, or hydrophobic
with hydrophilic particles attached. For example, WATERLOCK polymer
(Grain Processing Corp., Muscatine, Iowa) can be incorporated into a
highly hydrophilic bandage that can hold up to 60 times its dry weight of
water or more. Such an elastomeric, water-containing wound dressing
material may provide a reservoir of water, fluid flow driven by
alternating compression and expansion of the bandage, transport of
therapeutic substances to the wound and transport of soluble or
water-transportable by-products of healing away from the wound.

[0038]It is envisioned that the proportion of each component in the
non-woven fiber assembly may vary according to the particular
requirements of a specific type of use. It is also envisioned that the
proportion of each component in the dressing may vary within the
non-woven fiber assembly itself such that the composition of the assembly
on one surface differs from the composition of the assembly on another
surface. For example, one or more fibers made primarily of an elastomeric
polymer may form a surface of the dressing furthest from a wound. The
percentage of elastomeric polymer present in fiber in this portion of the
dressing may approach and include 100 percent. In the interior of the
dressing, fiber with an increasing amount of a hydrophilic polymer may be
present. The percentage of hydrophilic polymer present in fiber in this
portion of the dressing may approach and include 100 percent. The
thickness of this portion of the dressing may also vary according to the
anticipated needs of a particular application. The fiber on the surface
of the dressing to be placed in contact with the patient may contain an
increasing amount of polymer having adhesive properties. The percentage
of adhesive polymer used in fiber in this portion of the dressing will
vary with the need for aggressive or non-aggressive adhesion, but may
approach and include 100 percent. The transition from one type of polymer
to another may be gradual, producing no distinct layers of fiber type
within the dressing, or the transition may be abrupt, thereby producing
distinct layers within the dressing. The polymer fiber may be applied in
a sterile condition. Alternatively, the composition of the at least one
fiber may be constant along the length of the fiber.

[0039]As described more fully below, the hydrophilic component, when
contacted with water, is believed to absorb the water and to expand,
thereby surrounding the adhesive component, keeping the adhesive from
adhering to the surface of the wound. The hydrophilic component also
keeps the dressing moist, facilitates movement of water to the external
surface of the dressing, and facilitates the movement of therapeutic
substances throughout the dressing. Examples of suitable hydrophilic
polymers include, but are not limited to, linear poly(ethylenimine),
cellulose acetate and other grafted cellulosics,
poly(hydroxyethylmethacrylate), poly(ethyleneoxide), poly
vinylpyrrolidone, polyurethanes, polypropyleneoxides and mixtures and
co-polymers thereof. The hydrophilic component may also be a water
absorbing gel such as WATERLOCK polymer or carboxymethyl cellulose. The
hydrophilic component may be incorporated into the fiber, attached to the
surface of the fiber, or physically held between fibers.

[0040]The elastomeric component of the present invention provides
mechanical strength to the dressing and that ability to conform to
stretching of the skin. Mechanical strength is needed not only to hold
the assembly in place during use, but also to facilitate removal of the
dressing when it needs to be changed. Examples of suitable elastomeric
polymers include polyurethanes, polyesters, polyanhydrides, polyamides,
polyimides and mixtures and co-polymers thereof.

[0041]Adhesive components are needed to adhere the assembly to a
substrate. Suitable polymers having adhesive properties include
homo-polymers and co-polymers of acrylates, polyvinylpyrollidones, and
silicones and mixtures thereof. The adhesive may be a fiber that forms an
open network, attaching the dressing to the wound at many points, but
allowing essential passage of fluids through interstices in the adhesive
network.

[0042]The polymers contained in the fiber may also contribute to more than
one component category. For example, an acrylate-block co-polymer may be
used. In such a case, the acrylate block contributes adhesive properties
while the co-polymer block contributes hydrophilic properties.

[0043]While not wishing to condition patentability on any particular
mechanism of action, it is believed that the components of the
fiber-forming polymers create structures internal to the fibers by phase
separation that are in the form of rods, particles, sheets or other
geometrical forms. It is also believed that upon wetting, the hydrophilic
component may swell and expand in a way that physically prevents the
adhesive component from coming in contact with a substrate surface.
Thereby, a medical dressing of the present invention will adhere to
undamaged skin, because the hydrophilic polymer has not been contacted by
water and has not swollen to surround the adhesive component. The
dressing will not adhere to a wound or tissue at an early stage of
healing, on the other hand, because moisture from the wound contacts the
hydrophilic component causing it to swell and interfere with the
adherence of the adhesive to the wound.

[0044]In the same way, deliberate wetting of a part of the dressing that
would otherwise adhere to the skin will cause the hydrophilic regions to
swell. Such wetting and swelling makes the bandage easy to remove.
Preferably, inadvertent wetting is avoided to keep the bandage in place.

[0045]The non-woven fiber assembly may also be used for other
applications. For example, the fiber assembly may be utilized to deliver
pesticides, nutrients or other desired compounds to crops. The fiber
assembly would adhere to the crops when dry, but could be readily removed
by washing with water. The assembly may also be used as a type of sponge
or wall-less flask to absorb or contain water or other liquids. The fiber
assembly would therefore be useful in diapers, personal hygiene products,
absorbent towels and the like.

[0046]The present invention also provides a method of making a non-woven
fiber assembly, the method comprising the steps of providing at least one
fiber-forming material containing an adhesive component, an elastomeric
component, and a hydrophilic component, and forming at least one fiber
from the fiber-forming material. The fiber assembly of the present
invention may be formed from soluble polymers in either organic or
aqueous solvents. The fiber-forming material may be provided in a solvent
such as an alcohol, ethyl acetate, acetone, or tetrahydrofuran (THF), for
example. It may be desired in some applications that the solvent be
biologically compatible.

[0047]The method may optionally include a treatment step following
formation of the fibers to provide a desired property to the dressing.
For example, fiber containing a water-soluble material may be
cross-linked to form water-insoluble fibers. In another example, the
fiber may be treated to include a therapeutic or pharmaceutical product.
Linear polyethylenimine may be treated with nitric oxide to form linear
polyethylenimine diazeniumdiolate, for example.

[0048]As mentioned above, the relative amounts of the adhesive component,
the elastomeric component, and the hydrophilic component may vary over
time during fiber formation, producing a medical dressing or other
non-woven fiber assembly in which the composition at a first surface
differs from the composition at a second surface. For example, one or
more fibers may be electrospun primarily from an elastomeric polymer to
form a surface of a medical dressing that will not contact the patient.
As fiber is electro-spun to form the interior of the dressing, an
increasing amount of a hydrophilic polymer is used to form the fiber.
After a sufficient amount of fiber containing hydrophilic polymer is
incorporated into the dressing, an increasing amount of polymer having
adhesive properties is used to form the fiber of the dressing. The
transition from one type of polymer to another may be gradual (i.e.--a
constant gradient between polymer types), producing no distinct layers of
fiber type within the dressing, or the transition may be abrupt (a step
gradient between polymer types), thereby producing distinct layers within
the dressing. The transition between regions of the dressing may also be
the result of a non-constant or "skewed" gradient between polymer types.
Other variations or combinations of transitions may be used in this
method. Also, the layers in the center of the dressing may differ from
those in other parts of the bandage by controlling the position of the
fiber jet with an electric field or air currents, for example.

[0049]In one particular embodiment, a medical dressing is made according
to the following method. At least one fiber is electrospun from an
elastomeric polymer, such as elastomeric polyurethane, under conditions
that produce a wet fiber, that is, a fiber containing excess solvent,
either within the entirety of the fiber or only on the surface of the
fiber. The wet fiber or fibers are collected on a receiver such as a
non-stick film. The collected wet fiber will melt or fuse at places of
intersection without sintering at high temperatures, to form a fibrous
film with high water vapor transmission rate and air permeability. The
conditions for electrospinning are then changed such that a dry fiber is
received over the wet fiber. This may be accomplished, for example, by
increasing the distance between the electrospinning device and the
receiver. When a layer of dry fiber is laid down on the wet fiber, the
composition of the polymer is changed to a hydrophilic polymer, such as a
hydrophilic polyurethane. This second polymer may be introduced by a step
gradient, a constant gradient, or a skewed gradient between polymer
types. The concentration of hydrophilic polymer may approach or equal 100
percent. A predetermined amount of fiber is deposited and the composition
of the polymer is then changed to an adhesive polymer. As with the
previous transition between polymer types, the transition may occur via a
step gradient, a constant gradient, or a skewed gradient between polymer
types. The composition of this portion of the dressing may approach or
equal 100 percent adhesive polymer. The adhesive polymer forms the
surface of the dressing that is applied to the patient.

[0050]The present invention likewise provides a method of treating a
patient comprising applying a medical dressing to a predetermined area of
a patient, wherein the dressing contains one or more fibers and contains
an adhesive component, an elastomeric component, and a hydrophilic
component. This method may be used to apply one or more fibers to a burn,
a wound or another area needing protection from contamination or an area
requiring treatment with therapeutic or pharmaceutical compounds. The
method may include forming the at least one fiber on a separate receiver
and then transferring the at least one fiber to the predetermined area of
the patient, or applying the at least one fiber directly onto the
predetermined area.

[0051]As suggested hereinabove, other additives, either soluble additives
or insoluble particulates, may also be included in the liquid(s) to be
formed into the at least one fiber. Preferably, these additives are
medically important topical additives provided in at least
therapeutically effective amounts for the treatment of the patient. Such
amounts depend greatly on the type of additive and the physical
characteristics of the wound as well as the patient. Generally, however,
such additives can be incorporated in the fiber in amounts ranging from
trace amounts (less than 0.1 parts by weight per 100 parts polymer) to
500 parts by weight per 100 parts polymer, or more. Examples of such
therapeutic additives include, but are not limited to, antimicrobial
additives such as silver-containing antimicrobial agents, and
antimicrobial polypeptides, analgesics such as lidocaine, soluble or
insoluble antibiotics such as neomycin, thrombogenic compounds, nitric
oxide releasing compounds that promote wound healing such as sydnonimines
and diazeniumdiolates, bacteriocidal compounds, fungicidal compounds,
anti-viral compounds, bacteriostatic compounds, anti-inflammatory
compounds, anti-helminthic compounds, anti-arrhythmic compounds,
antidepressants, antidiabetics, antiepileptics, antimuscarinics,
antimycobacterial compounds, antineoplastic compounds,
immunosuppressants, anxiolytic sedatives, astringents, beta-adrenoceptor
blocking compounds, corticosteroids, cough suppressants, diagnostic
compounds, diuretics, antiparkinsonian compounds, immunological
compounds, muscle relaxants, vasodialators, hormones including steroids,
parasympathomimetic compounds, radiopharmaceuticals, antihistamines and
other antiallergic compounds, anti-inflammatory compounds such as PDE IV
inhibitors, neurohormone inhibitors such as NK3 inhibitors, stress
protein inhibitors such as p38/NK/CSBP/mHOG1 inhibitors, antipsychotics,
and xanthines, adhesives, fragrances, odor absorbing compounds, and
nucleic acids such as deoxyribonucleic acid, ribonucleic acid, and
nucleotide analogs, enzymes and other proteins and growth factors.

[0052]In still another embodiment, additives that contribute to the
structural properties of the article may be included in the medical
dressing. These include small solid particles, dispersed droplets of
immiscible liquids in which other substances may be dissolved,
crosslinking compounds, blowing agents to create foams, adhesives,
elastomers and the like, which may be chosen for their function in
protecting and healing the wound.

[0053]It will be appreciated that a number of different types of membranes
may be produced according to the present invention, depending upon how
the fibers are produced and deposited. In one embodiment, the liquid to
be formed into fiber is a mixture of an adhesive polymer, a hydrophilic
polymer, and an elastomeric polymer. Thus, one fluid could provide the
entire membrane. However, it is also envisioned that composite fibers of
different compositions could be spun together or in sequential layers to
provide a suitable membrane.

[0054]The method of using the medical dressing of the present invention
may comprise applying at least one fiber to a wound or other area needing
protection from contamination, or an area requiring treatment with
therapeutic or pharmaceutical compounds, to form a fibrous non-woven
matrix, wherein the dressing comprises a hydrophilic component, an
elastomeric component and an adhesive component.

[0055]In another embodiment, the dressing additionally comprises at least
one pharmaceutical or therapeutical agent selected from the group
consisting of antibiotic compounds such as bacteriocidal and fungicidal
compounds, bacteriostatic compounds, crosslinking compounds, analgesic
compounds, thrombogenic compounds, nitric oxide releasing compounds such
as sydnonimines and diazeniumdiolates that promote wound healing, other
pharmaceutical compounds, adhesives, fragrances, odor absorbing
compounds, and nucleic acids, without regard to solubility in a
biocompatible solvent. In contrast to previous electrospun fibers, the
additives are not limited to those that are soluble in the
polymer/solvent combination. It has been discovered that even insoluble
additives that may be added to the polymer/solvent combination of the
present invention remain within the fiber.

[0056]Finally, the present invention also provides an apparatus for
forming at least one composite fiber, the fiber comprising a hydrophilic
component, an elastomeric component and an adhesive component. The
apparatus comprises a plurality of reservoirs for containing more than
one type of fiber-forming material, a plurality of valves each
independently in communication with a reservoir, and a fiber-forming
device selected from the group consisting of a spinnerette, a NGJ nozzle,
and an electrospinning device, in communication with said valves.

[0057]An embodiment of the apparatus of the present invention may be
described with reference to the figure. Apparatus 10 comprises a first
reservoir 12, a second reservoir 16 and a third reservoir 20. First
reservoir 12 is in fluid communication with a first valve 14. Likewise,
second reservoir 16 is in fluid communication with a second valve 18 and
third reservoir 20 is in fluid communication with a third valve 22.
First, second, and third valves 14, 18, and 22 may be manually controlled
or they may be placed in communication with a controller 24 for automated
control. First, second, and third valves 14, 18, and 22 are optionally in
communication with a mixing chamber 26, which is, in turn, in
communication with a fiber-forming device 28. Alternatively, a spinning
device (spinnerette, NGJ nozzle, electrospinning apparatus) may be
attached to each reservoir. The rate of fiber production from each device
may be regulated to supply the particular polymer in the amount needed to
produce the desired spatially variable structure. When the fiber-forming
device is an electrospinning device, a power source is in electrical
communication with the electrospinning device.

[0058]Apparatus 10 may be used to form fibers according to the present
invention by placing an adhesive component, an elastomeric component, and
a hydrophilic component in each of the reservoirs 12, 16, and 20. The
relative amounts of each component fed to fiber forming device 28 is
controlled by selectively opening or closing each of valves 14, 18, and
22. The relative amounts of each component controls the composition of
the fibers produced by fiber-forming device 28.

[0059]In order to demonstrate the practice of the present invention,
composite fibers were electrospun from a THF:ethanol solution (30:70)
containing WATERLOCK A-180 and TECOPHILIC polymers to form non-woven
fiber assemblies or mats. WATERLOCK polymers are corn
starch/acrylamide/sodium acrylate copolymers available from Grain
Processing Corp. (Muscatine, Iowa). WATERLOCK polymers contribute a
hydrophilic component to the resulting fiber assembly. TECOPHILIC is an
aliphatic polyether-based polyurethane available from Thermedics Polymer
Products (Wilmington, Mass.), which contributes an elastomeric component
and a hydrophilic component to the fiber assembly. Mats of fibers
containing 7, 30, 50, 70, or 85 percent WATERLOCK (WL) were tested for
their absorbency against the absorbency of a mat containing fibers with
no WATERLOCK. The equilibrium water content was determined by soaking the
fiber mats in distilled water for 24 hours at room temperature and
comparing the weight of the mat before and after soaking. The percentage
of weight gain for each sample is shown graphically in FIG. 2. FIG. 2
shows that addition of WATERLOCK polymer greatly increases the absorbency
of the resulting fiber assembly.

[0060]Samples containing WATERLOCK and TECOPHILIC polymers were also
tested for their stress-strain behavior. The samples were tested on an
Instron fatigue test system model 5567 (Canton, Mass.) using an ASTM 638
pattern. The samples were stretched at a rate of 50 mm/min. The
stress-strain behavior of samples containing 7, 30, 50, 70, or 85 percent
WATERLOCK (WL) is shown in FIG. 3. According to these data, the amount of
deformation (strain) that the samples could absorb exceeded 500% in each
case. The tensile strength of the fiber assembly was greatest with 7
percent WATERLOCK, which was also greater than the sample consisting of
TECOPHILIC polymer (0% WL).

[0061]In this specification and the appended claims, the singular forms
"a," "an," and "the" include plural reference unless the context clearly
dictates otherwise. Unless defined otherwise, all technical and
scientific terms used herein have the same meaning as commonly understood
to one of ordinary skill in the art to which this invention pertains.

[0062]Based upon the foregoing disclosure, it should now be apparent that
the medical dressing of the present invention will carry out the objects
set forth hereinabove. It is, therefore, to be understood that any
variations evident fall within the scope of the claimed invention and
thus, the selection of specific component elements can be determined
without departing from the spirit of the invention herein disclosed and
described.